Electrosurgery involves the application of radio frequency electrical energy to tissue. The electrical energy originates from an electrosurgical generator (ESG) and is applied by an active electrode to the tissue. The active electrode typically has a small cross-sectional or limited surface area to concentrate the electrical energy at the surgical site. An inactive return electrode or patient plate contacts the patient at a remote location from the surgical site to complete the circuit through the tissue to the ESG. The patient plate is relatively large in size to avoid destructive energy concentrations. Alternatively, a pair of active electrodes may be used in a "bipolar" mode in which the electrosurgical energy flows directly through the tissue between the two active electrodes, and the electrosurgical effects are confined to the tissue directly located between the two closely-spaced electrodes.
A variety of different electrosurgical effects can be achieved, depending primarily on the characteristics of the electrical energy delivered from the ESG. Among the effects are a pure cutting effect, a combined cutting and hemostasis effect, a fulguration effect and a desiccation effect. Desiccation and fulguration are usually described collectively as coagulation. Many conventional ESG's offer the capability to selectively change the energy delivery characteristics and thus change the electrosurgical effects created.
Satisfactory fulguration effects have been particularly difficult to obtain. Some surgeons have preferred to use older spark gap generators known as "Bovie" devices for fulguration, but use other more modern ESG's for cutting or cutting with hemostasis. Indeed, spark gap ESG's have been the standard against which modern solid state ESG's have been measured for achievement of satisfactory fulguration effects. One modern ESG which achieves substantially improved fulguration effects, compared to both spark gap and previous solid state ESG's is described in U.S. Pat. No. 4,429,694, assigned to the assignee hereof. Despite the improvements available in fulguration, certain disadvantages remain for which there have been no satisfactory alternatives.
Conventional fulguration is characterized by electrical arcing through the air from various locations on the metal surface of the active electrode, with the arcs contacting the tissue in somewhat of a random non-predictable manner. In many cases, arcs leave the active electrode in an initial trajectory traveling away from the tissue before actually curving around and striking the tissue surface. The result is an uneven, randomly concentrated or distributed delivery of arcing energy. An uneven eschar of variable characteristics is created on the surface of the tissue, as is exemplified by the eschar shown in FIGS. 1, 2, 3A and 3B. The characteristics of the prior art eschar have been studied as a part of the present invention. Even though such characteristics have probably existed for some considerable time, and therefore are prior art, the development of the present invention has resulted in what is believed to be the first relatively complete understanding of the prior art eschar and the practical coagulation or hemostatic consequences of it.
The random delivery of the arc energy creates holes which are significantly disparate in diameter (or cross-sectional size) and in depth, as is shown in FIGS. 1, 2, 3A and 3B. The larger, deeper holes are formed by repeated arcs contacting the tissue at approximately the same location. The smaller arc holes are also present in the tissue but they are unevenly distributed about the larger arc holes. The smaller arc holes are created by single individual arcs, or the less repetitious arcing to the tissue at the same location. The smaller arc holes are relatively small in diameter or cross-section and relatively shallow in depth, compared to the larger arc holes. Significant variations in cross-sectional size and depth between the large and small arc holes occur. Significant variations exist in the spacing and in the amounts of tissue between the large and small arc holes, causing the substantial variations in the surface distribution of the holes.
Thermal necrosis occurs in the tissue between the arc holes. The degree of thermal necrosis varies between total carbonization between the more closely spaced larger holes, to necrosis without charring or carbonization between the more widely separated smaller arc holes.
The eschar created has two distinct layers above the unaffected viable tissue. An arc hole reticulum of the tissue subjected to necrosis is created by the pattern of arc holes, and this arc hole reticulum extends to a depth or layer referenced 30 as shown in FIGS. 3A and 3B. The arc hole reticulum 30 extends to greater depths in the areas of the deeper arc holes, and to substantially shallower depths in the areas of the shallower arc holes. Due to the random distribution and depth of the arc holes, the arc hole reticulum is relatively uneven in depth. Significant variations in the depth of the arc hole reticulum layer are typical. A layer 32 of thermally desiccated tissue is located below the arc hole reticulum layer 30. Tissue necrosis in the layer 32 occurs as a result of desiccation due to the current heating effects of the electrical energy dissipating from the arcs. The desiccation layer 32 is also uneven in depth and location due to the nonuniform application of the arcing energy over the arc hole reticulum layer 30. Significant variations in the depths of the desiccation layer are also typical.
Over a given area of tissue, certain locations such as those shown on the right hand side in FIG. 3A are only moderately affected by the arcing energy. A thin arc hole reticulum and a thin desiccation layer result. Other areas, such as those shown on the left hand side of FIG. 3B, have a relatively thick eschar formed therein. Very thick carbonized eschars tend to be fragile and are prone to crack when flexed, usually resulting in renewed bleeding from the unaffected tissue at 34 below the desiccation layer. Thin eschars are more flexibile and therefore more desirable, but it has been difficult to obtain sufficient coagulation effects from thin eschars.
Causes of the uneven eschar created by prior fulguration techniques are not known with certainty, but numerous factors are theorized to play a role. One of the more significant contributory factors is probably changes in impedance in the arc pathway between the active electrode and the tissue. Impedance changes may result from variations in the distance which the arcs travel through the air, due to the changes in ionization potential between the active electrode and the tissue. It is virtually impossible for the surgeon to maintain the active electrode at a consistent distance from the tissue, particularly if the tissue is moving due to pulsation, or due to puckering and swelling as a result of applying the electrical energy. The arcing from random locations on the active electrode also creates different arc length pathways and hence impedances. The combined impedance of the tissue and the eschar changes with the application of electrical energy. The volatilization of the cells and vaporization of the moisture in the cells changes the relative impedance in a localized spot-to-spot manner on the surface of the tissue. The formation of the charred material also influences the arc pathways, presenting an opportunity for subsequent arcs to return to the tissue at the same location and thereby enlarge the pre-existing arc hole and create even further charring.
Another problem with conventional electrosurgery is that it is very difficult if not impossible to achieve effective fulguration on spongy or vascular tissue such as the liver or the spleen, or on other tissues from which there is a tendency for blood to continually ooze over the surface from the highly developed vascular network within the tissue. Often, only the surface of the oozing blood is coagulated, with no penetration to the surface of the tissue below the layer of blood. A superficial coagulum results on the surface of the blood, but this coagulum quickly sloughs away resulting in only temporary hemostasis. Of course, once the temporary coagulum sloughs away, bleeding continues. Even if a coagulation effect on the tissue surface can be established, it is easily destroyed or perforated by the arcs returning to the same locations causing the longer, deeper arc holes. The deeper arc holes perforate the eschar and extend into the viable tissue below the eschar to provide a pathway for continued bleeding. The heat created by the arcs causes boiling of moisture below the eschar, and the pressure of resulting vapor can also rupture the eschar to reinitiate bleeding.
Apart from the tissue disadvantages of conventional electrosurgical fulguration, certain other practical problems exist. Arcing from the active electrode rapidly increases the temperature of the active electrode. Electrode heating is responsible for a number of problems. If the heated active electrode contacts the tissue, as it inevitably will, or if the active electrode is immersed in fluid such as blood, proteins from the tissue or the blood are denatured and stick to the active surface of the electrode. The buildup of charred material on the electrode eventually creates a sufficiently high impedance so that adequate power can no longer be delivered. The surgeon must continually clean the electrode by wiping or scraping the charred material, which disrupts, distracts, and prolongs the surgical operation. Freshly created eschars can be detached in an effort to free a sticking electrode from the tissue surface. The random accumulation of charred material on the active electrode creates more random delivery of the arcing energy, even further increasing the random delivery pattern. Because of the variable nature of the impedance of the charred material, consistent power application is difficult or impossible. The accumulation of the charred material can obscure the surgeons view of the surgical site. The temperature of the active electrode may reach sufficiently elevated levels to transfer molten metal from the electrode to the patient, creating questionable effects. Because the electrode contacts the tissue, there is a potential for cross-contamination between viable tissues and diseased tissues. Although the clinical problems associated with cross contamination are not fully understood at the present time, the advantages of eliminating the possibility are evident. A significant smoke plume also results from the burning tissue because of the air environment in which the electrosurgery occurs. Not only does the plume produce a noxious odor, but there may be some evidence that particulates in the smoke plume from burning tissue may contain hazardous chemicals, virus, bacteria, neoplastic cells and other hazards. Of course, the oxygen environment in which the electrosurgy is conventionally conducted exhibits a potential for igniting paper drapes, surgical sponges and the like.
Some of the typical problems associated with creating and applying the arcs in conventional electrosurgery can be improved by optimizing the operating and other characteristics of the electrosurgical generator. U.S. Pat. No. 4,429,694 discloses an improved ESG which reduces some of the described disadvantages during fulguration. However, many of the disadvantages cannot be avoided and many of the characteristics cannot be improved by conventional electrosurgical techniques and equipment, due to the limitations previously inherent in electrosurgery.
The conventional technique of obtaining thermal desiccation by use of a conventional ESG is to apply electrical energy from a flat surface of the active electrode placed in contact with the tissue. An electrical resistance heating effect is created by the current flowing into the tissue from the active electrode. Because the active electrode contacts the tissue surface over a relatively large area, no arcing is intended to occur. To spread the thermal desiccation effect over a substantially large area, the active electrode is moved from location to location. It is very difficult to apply a level of energy which will obtain thermal desiccation but which will not cause the tissue to stick on the flat surface of the active electrode or arcing from the active electrode to non-contacted surface areas. The thermal desiccation effects are unevenly distributed because the active electrode is moved from spot to spot. Overlapping the spots of energy application can enhance the probability for tissue sticking and exaggerate the variable depth effects. Of course, moving the active electrode from spot to spot is very time consuming in an operation where time is very important or critical.
The prior art desiccation technique can only be applied to create surface desiccation effects. Furthermore, the inability to accurately control the amount of power, tissue sticking effects, and the like have prevented the prior use of electrosurgery on very thin fragile tissue such as the mesentary, and in other surgical techniques.
It is against this abbreviated background of previously existing disadvantages and problems in electrosurgery that the advantages and improvements of the present invention can be better appreciated.